\begin{table}[!htb]\centering                  \def\sym#1{\ifmmode^{#1}\else\(^{#1}\)\fi}                   \caption{Dataset Composition\label{tab:appendix_table}}                 \setlength{\tabcolsep}{1pt}                                  \begin{tabular}{l*{3}{c}}\hline\hline
                &      All&    Merge& Estimating sample\\
\hline
HMPS Sample 1992-2008\\\hline
N               &      816&      815&      575\\
Segments        &  257,490&  257,490&  186,055\\
Lane Miles      &3,462,979&3,462,979&2,389,689\\
\hline
Highway Statistics 1992-2008 \\\hline
N            &      816&      815&      575\\
Total Expenditure           &  292,732&  292,220&  216,780\\
Maintenance&   60,170&   60,170&   44,473\\
Resurfacing&  116,158&  116,044&   89,393\\
Construction&  116,404&  116,006&   82,914\\
\hline
HPSM Universe 1984-2008\\ \hline
N               &    1,200&    1,200&    1,171\\
Lane Miles      &5,012,646&5,012,646&4,929,418\\
\hline
Highway Statistics 1984-200\\\hline
N            &    1,200&    1,200&    1,171\\
Total Expenditure           &  395,296&  395,296&  395,295\\
Maintenance&   83,729&   83,729&   83,729\\
Resurfacing&  148,777&  148,777&  148,777\\
Construction&  162,790&  162,790&  162,790\\
\hline\hline                 \multicolumn{4}{}{ \footnotesize . . }                 \end{tabular}\end{table}
